Telephone system



June 2, 1931..` G, BABCOCK 1,808,280

TELPHONE SYSTEM Fid July 29. 1929 circuit.

Patented .lune Z, 1931 UNITED STATES PATENT oFFicE i GARR-ISDN BABCOCK, 0F SEATTLE, WASHINGTON, ASSIGNOR TO AMERICAN TEL- CHRONOMETER COMPANY, OF SEATTLE, WASHINGTON, A CORPORATION 0F VASI-I- INGTON TELEPHONE SYSTEM Application led July 2B, 1929. Serial No. 381,731.

rlhis invention relates to telephone substations and has for its principal object the provision of a new and improved telephone substation.

Telephone substation devices heretofore have commonly used a bell or ringer operated by alternating current to signal the subscriber and inform him of an vincoming call.

The ringing of a bell forms a desirable signal in a great many instances but there are locations in which such a signal is objectionable and various ways and means are employed to muiile its tone and thereby make the ringing of the bell less objectionable. For example; in hospitals, private offices, and many residences it is the common practice to muiile the gongs of the telephone ringer so that When the substation is rung the sound emitting from it is very greatly reduced. p

In my present invention I have provided a new and improved substation and central station equipment cooperating therewith toV permit a musical note to be transmitted through the receiver of the substation to act as a signal in place of the usual bells or ringer.

In one embodiment of my invention, I provide a tuned relay in the substation which is operated by the ringing current of the usual frequency. The operation of this relay connects the receiver of the substation and a condenser in series across the line At the'central oc'e I have provided a tone generator capable of generating a musical note or tone of audible frequency, and have provided circuits for superimposing that tone upon the ringing current under the control of the ringing key' in the cross circuit.

This tone traversing the line circuit is projected through the receiver and condenser in series therewith and causes the receiver to reproduce the tone audibly.

By this arrangement, the telephone substation is signalled by a musical note of only suilicient volume to enable it to be heard in the immediate vicinity'of the telephone.

The particular embodiment in which the tuned relay is employed is adaptable for party line systems wherein the substations on the line are selected by ringing current of different frequencies, each relay being tuned to respond to only one of those frequencies to connect one of the receivers across the line. The tone source is common to all of the parties on the line and projects through only the receiver corresponding to the energized tuned relay.

As a further object of my invention I have provided a tuned relay designed in such a manner that it serves not only as a relay for connecting the receiver across the line during the ringing period, but also vserves as an induction coil to augmentV the undulations in the line current produced by the resistance variations in the transmitter and thereby produce what vis commonly known as the boostertype substation circuit.

To this end I have employed a transmitter of the push pull type, one terminal of which is connectedto the midpoint of two of the windings of the tuned relay, and the other two points to the ends of two other windings of that relay. These two windings are connected to the relay in opposition to each other and their free ends are adapted to be connected across the line in series with the receiver and in multiple with the first two windings of the relay by the hook switch or other switching means at the telephone. y

By this arrangement the telephone substation is simplified in that the tuned relay serves also as an induction coil and the ringer which is customary in such stations of this kind is omitted entirely. The relay `may be mounted in the base of a desk telephone and the usual bell box eliminated from the installation.

NOW to acquaint those skilled in the art with the teachings of my invention, reference is made to the accompanying drawing in which I have illustrated a preferred embodiment of it.

In this drawing that equipment below the dot dash line is assumed to be in the central office C, and the line l, 2 leading therefrom is assumed to be a party line upon which rent type through the windings of which thel transmitted feed current is conducted. This receiver is not provided with a permanentk magnet and the magneto-motive force set up in its Winding by the transmitter current is relied upon to furnish magnetism for operationfofthe receiver. .Y

The transmitter 4 is of the push pull type having the main diaphragm V9 and microphone cells 10 and 11 which are'disposed onopposite sides of this diaphragm. The diaphragm and microphones are incased in a suitable housing opposite anv opening in which the mouth piece 12,.is fittedY to permit vibration set up by speech to act upon the diaphragm and thereby actuate the transmitter.

The relay-induction coil 5 comprisesthe U-shaped magnetic iron core13 upon. the

opposite legs of which Vare wound` the windings 14 and 15. These windings are ofY equal values bothas to resistance and number of turns and are so .placed and connected together that current flowing through them 1ny series builds up magnetomotlve forcesin the two legs of the core 13 in: suchY directions that these forces assist each.v other in driving flux through the core. Y

Windings 16 and 17 also disposed. upon the magnetic core 13 are likewise of equal resistance and equal number of turns,these coils preferably being of lower resistance than the coils and 16. Nindings 1GL and 17 are connected in circuit` with the microphones 10 and. 11 ofthe transmitter 4 in such direction that during the Voperation of the transmitter the magnetomotivet force set up in the winding 1G opposes the magnetomotive force set up in the winding 17.

The relay 5 is provided with an armature 18 whichis pivoted at its midpoint 19 and provided with -a `tuning weight 2O z through the adjustment of which` thearmature is made responsive to alternating current of a particular frequency and prevented from responding to .alternating currents of other frequencies. The armature 18 carries springs 21 and 22 disposed at its opposite free ends and adaptedwhen moving to engage springs 23 and 24 and 25l and. 26 respectively.

The circuits of the substation includethe normally closed yalternating current circuit extending from the junction 31 of the line conductor 2 through the winding .14 of the relay 5 and the winding 15 of that relay through the spring 32 and its break contact through the condenser 7 to the line conductor .1. V By this circuit the relay windings 1.4 and 15 are bridged across the line in series with the conductor 7.

It is over this circuit'that the selective ringing takes place.

At the central oii'ice C, the cord circuit CC which may be any preferred type of cord circuit-or in the case of an automatic telephone exchangea final selector or connector, comprises .the means CP which together with the calling jack CJ establishes ai circuit wit-h the line conductors 1, 2 leadingI to the substationA.

Associated with the cord circuit @C is the Vringing key RK. throughV the operation ofwhichv the generators 50, 51,52, 53 and 54 are connected tothe cord circuit in series with the induction coil winding 55. Only one of these generators to 54 is connected to the cord circuit at; av time, selection being-v controlledL by the key springs-56, 57, 58,59 and 60. s

The tone source 61 whichl maybe an audion oscillator, a1 Vreeland oscillator, or any other preferred type of electrical' or mechanical oscillator capable of producing a musical note of approximately 1,000 cycles frequency,` is connected by wires A62 and 63 `to opposite terminals of theprimary winding 64 of the induction coil.

Assume now, that the relay 5- is tuned to respond to ay frequency of 16 cycles persecond, and that the generator 50' is capable of producing that frequency, to signalthe` substation A, the operatorinserts the calling plug CP inthe carlling jack GJ and operates theV ringing key RK toy connect theV ringing current to the cord circuit. She also operates the key spring156tofs'elect the'pa-rticular frequency ofringingcurrent tobe `applied to theline.A The circuit may now be traced ,fromz one pole of the generator 50 thro-ugh the key spring 56,Y through. the upper ring- V ingkey spring 65andiits make Contact,

through the tip of the-plug and jack GP and CJ to the'A line conductor 1 through the condenser 7, thence throughl spring 32 and its break. contact, through the coils 15 and 14 of the relay 5, the junction 31 and the line conductor 2, to the ring section of the jack i and plug CJ and CP through the spring 66 of the ringing key RK and its make contact through the winding 55 of the induction coil and to the opposite terminal ofthe generatoll 50.

The relay 5 is operated over this circuit and its armature 18 vibrated in synchronism with the 16 cycle current thus projected, it being remembered' that this particular` relay is tuned to respond only to 16 cycle f current.

The oscillation of the armature 18 of the relay 5 connects the springs 21 and 22 to their respective springs 23 and 24 and 25 and 26 alternately to close a circuit from the line conductors 2 and the junction 31 thereof through those springs and armature, through the condenser 8, the receiver 3, to the line conductor 1.

The musical note of aproximately 1,000 cycles frequency generated 'by the tone source 61 and made to traverse the primary winding 64 of the induction coil induces in the secondary winding 55 of that induction coil a tone of similar frequency which is superimposed on the ringing current from the generator 50 over the circuit just traced. This high frequency tone traverses the circuit through the armature 18 and condenser 8 and receiver 3 of the substation and causes the receiver 3 to move its diaphragm in synchronism with the frequency of that tone source. This causes the receiver to emit a musical note of approximately 1,000 cycle frequency and of sufficient intensity to enable it to be heard within the immediate en virons of the telephone. This noteacts as a signal to inform the subscriber at the telephone that an incoming call is on his line.

The subscriber upon hearing this signal answers the call by lifting the receiver 3 from the hook switch 6, the removal of the weight of the receiver from this hook switch causing it to assume the position shown in the dotted line and in which the spring 32 is made to break away from its break con-I tact and make a connection with its make contact. Similarly spring 33 is caused to close a circuit through its make contact and spring 34 to likewise close a circuit through its make contact.

The operation of spring 32 responsive to the removal of the receiver 3 from the hook switch 6 removes the condenser 7 from the bridge across the line circuit at the substation and substitutes therefor, the two windings 14 and 15 of the relay 5 in series with the winding of the receiver 3. This substitution converts the substation bridge from an alternating current bridge into a direct current bridge and if the cord circuit CC is one equipped with automatic ringing control and instantaneous cut-off therefor, as would be the common practice in a modern telephone exchange, the substitution of this direct current bridge causes the application of ringing current to the line to be automaticaL ly terminated.

The operation of hook switch springs 34 as above pointed out closes the circuit from line conductor 2 through those springs and the winding 16 of the relay 5, through the microphones 10 and 11 of the transmitter L11 in series, through the winding 17 of the relay 5 to the spring 33, through the receiver 3 to the line conductor 1.

As has been previously pointed out the current flowing through the windings 14 and 15 of the relay 5 sets up therein magnetomotive forces which assist each other in driving flux through the core 13. Current flowing through the winding 16 sets up in thatwinding a magnetomotive force which assists the magnetoinotive forces of the windingsl and 15, while the current flowing through the winding 17 opposes the other magnetomotive forces in driving flux through the core.

When the subscriber speaks into the mouth piece 12 of the transmitter 4, the diaphragm 9 is moved back and forth adding tothe resistance of the microphone cell 10 and simultaneously subtracting from the resistance of the microphone 11 an equal amount. This action varies the current flowing through the windings 16 and 17 those variations being inverse related, that is when the current through winding 16 is increasing the current through winding 17 is decreasing at the same rate.

This variation of current through the windings 16 and 17 produces little or no effect upon the current flowing through the windings 14: and 15, those windings maintaining a practically constant flux flow through the core.

' The magnetomotive forces generated in Vthe coil 16 are opposed by those generated in the coil 17 and as the magnetomotive force in 16 is increasing the magnetomotivc force in 17 is decreasing so that the net result is a change in magnetomotive force, which increases the total flux flowing through the core 13. This change in flux induces in the windings 14 and 15 an alternating current in such a direction as to oppose the change of fluX and that alternating current flowing through the springs 32 and the receiver 3 augments the undulations in the line circuit produced by the resistance variations of the transmitter to thereby strengthen the voice currents transmitted over the line to the central olice.

When the current in winding 16 is decreasing and the current in winding 17 is increasing due to a vibration of tho diaphragm 9 in the opposite direction, Vthe inagnetoniotive` forces set up by those currents produce a change in flux in the core equal to twice the change produced by either winding 16 or 17, and thereby increases the total flux in the magnetic circuit of the core 13.

This induces in the windings 111 and 15 an electromotive force in the opposite direction which again augments the undulations of line current produced by the transmitter.

The cord circuit CC is shown as provided with the battery feed relay 67 and with the condensers 68 and 69, those units will be i cord circuit C and the answering plug Al) continue with their conversation and lupon the completion ofit subscriber at A replaces his receiver 3' on the hook switch 6 thereby breaking'the circuit closed through the make contacts of springs 32, 33 and''k and restoring; the substationL to normal. This restoration of the receiverto the lio-ol; switchV operates the customary supervisory relays Vin the cord circuit, or' supervisory circuits of the automatic telephone exchangeV if the substation be one of an automatic telephonel system, to cause that equipment to'be restored to normal in the well known manner.

When a subscriber at substation A desires to initiate a call, he removes his receiver from the switch hook thereby closing the direct current bridge previously traced to close a circuit from ground through the springs 70, line conductor l through the substation, to the line conductor 2 through the spring 7l and the winding of the line relay 72 to battery, energizing that relay which aty springs 73 closes a circuit through'the line lamp 74 to light that lamp and apprise the operator of the call. The operator upon noting the lighted lam-p inserts an answering plug such as AP into the answering jack AJ, thereby completing a circuit from battery through the answering supervisor relay, not shown, of the cord circuit and the sleeve of the plug AP, the sleeve 75 of the answering jack AJ, through to cut off. relay COR to ground to energize that relay, which at springs 70 and 7l removes battery and ground from the line conductors.

The particular type of line circuit equipment is not of the essence of the present invention, andany preferred equipment may be used in lieuv of that shown by way of example.

lVhil'e I have chosen to` show'my invention in connection with a party line substation in which the tuned relay is selected to connect the receiver across the line, have dene so-by way of example only, as the in-v vention may be applied to afstraight lineV substation in which the use of the tone relay is not necessary.

The ringing generators 50 to 54 are shown by way of example. only as any source of ringing current likely to be encountered in a telephone exchange may be employed instead of the generators shown.

Having thus complied with the statutes and having shown and described a preferred embodiment of myV invention, what select the )art f to be signaled and simultaneously 'applying a higher frequency tone superimposed on the low frequency current to Vsignal the selected station.

2. A telephone substation having the usual-*line circuit and talking instrumentalities, 'a relay in said substation having a:`

winding normally bridged across said line circuit in series with a condenser, an armature for said relay, said` armature being pivoted atl its midpoint and tuned to respond to only oneV frequency of alternating current, a contact spring mounted on .each freerend of said armature, a pair of springs adjacent each of said contact springs and adapted to be contacted thereby when. said armature is in Ymotion,` said' springs and armature closing a bridge across said line circuit andvincluding the receiver and a condenser in series.

3. In a party telephone system, a subscribers line having af plurality of stations` thereon, means at a'central oiiice for connecting any one of the plurality of frequencies of ringing current to that line, a relay at each station tuned to respond to current of a certain frequency, one' of said relays responding to said application of' current to select said station, a receiver at each station, said-energized relay connecting the receiver of that station to said line', and means for superimposing a tone on said ringing` current to actuate said receiver and thereby signal that station; Y

4. In a'telephone system, a relay having Vtwo windings normally connected across a line circuit in series with a condenser, a push pull transmitter having a midpoint connected to the midpoint ofsaid relay windings, a second pair of windings on said relay each of which has an end connected to an element of'said transmitter, la receiver, means' for disconnecting said first relay windings from said condenser and for connecting them across said line in series with said receiver, and-means for connecting the free ends of said second relaywindings in multiple withthe ends of said first windings to thereby conditionsaid substation for the transmission and reception of speech.

5.1n a telephone substation, a receiver, a relay, and a pair of condensers, a line circuit across which said relay and one of said :condensers are normally bridged, means associated with said line circuit for operating said relay thereover, and lmeans operated by the relay for bridging lsaid receiver and other condenser in multiple with said rst bridge and across said line circuit.

6. In a telephone substation, a receiver, a relay, and a pair of condensers, a line circuit across which said relay and one of said condensers are normally bridged, means associated with said line circuit for operating said relay thereover, and means operated by the relay for bridging said receiver and other condenser across said line circuit in multiple with said relay and first condenser.

7. In a telephone substation, a transmitter, a receiver, a relay, and a pair of condensers, a line circuit across which said relay and one of said Vcondensers are normally bridged, means associated with said line circuit for operating said relay thereover, means operated by the relay for bridging said receiver and other condenser in multiple with first bridge and across said line circuit, and means for bridging said line with a direct cross bridge including said relay and receiver in series with said transmitter in multiple with the relay.

8. In a telephone substation, a transmitter, a receiver, a relay, and a pair of condensers, a line circuit across which said relay and one of said condensers are normally bridged, means associated with said line circuit for operating said relay thereover, means operated by the relay for bridging said receiver and other condenser in multiple with said first bridge and across said line circuit, and manually controlled means at said substation for bridging said relay and receiver across said line in series and connecting said transmitter in multiple with said relay.

9. In a telephone system, a substation comprising a receiver, a relay having an armature tuned to respond to only one frequency of alternating current, a pair of condensers, a line circuit for said substation a normally closed alternating current bridge across said line circuit comprising said relay and one of said condensers in series, means associated with said line circuit for impressing alternating current thereon to operate said relay, means controlled by the armature of said relay for connecting said receiver and the other of said condensers across said line circuit, and means associated with said line for super imposing a second alternating current on said first to operate the receiver and thereby signal the subscriber at said station.

10. In a telephone system, a substation comprising a transmitter, a receiver, a hook switch, a relay having an armature tuned to respond to only one frequency of alternating current, a pair of condensers, a line circuit for said substation, a normally closed alternating current bridge across the line comprising said relay and one of said condensers in series, means associated with said line circuit for impressing alternating current thereon to operate said relay, means controlled by the armature of said relay for connecting said receiver and the other of said condensers across said line circuit, means associated with said line for superimposing a second alternating current on said first to operate said receiver and thereby signal a subscriber at said station, and means responsive to an operation of said hook switch for erasing the bridges established across said line circuit and for substituting a bridge including said relay, receiver, and transmitter.

l1. In a telephone system, a party line having a plurality of substations bridged across it, a relay at each substation', said relays being tuned to respond to dierent frequencies of alternating current, a receiver and a condenser at each substation, a cord circuit adapted to be connected to said line, a plurality of sources of alternating current associated with said cross circuit, said sources generating frequencies corresponding to said relays, a tone source associated with said cord, means for connecting one of said sources with said tone source superimposed thereon to said line circuit, the current from said source energizing one of said relays, and means controlled thereby to connect saidv receiver and condenser across said line, said superimposed tone source operating said receiver to signal said substation.

In witness whereof, I hereunto subscribe my name this 24th day of July, 1929.

GARRISON BABCOCK.

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